Keywords: 
• ultrasound /
• ultraviolet /
• disinfection /
• synergistic action

Abstract: There are many disadvantages in using traditional methods of disinfection for the WWTPs effluents and these are mainly due to the byproducts of disinfection. In this experiment,ultrasonic disinfection was studied as a means of exploring new disinfection technoloies suitable for treating the WWTPs effluents.The ultrasound of two different frequencies was used(21.51 kHz and 32.36 kHz)to investigate the inactivation of the total coliform bacteria by changing the factors such as the frequency of the ultrasound,the intensity and the irradiation time.The disinfectonal effect of the ultrasound and the synergistic action of US and UV were compared.The mechanism of ultrasonic disinfection is discussed.The results show that the disinfectional effect gets better with a longer disinfection irradiation time and a higher sound density.The disinfectional effect of using 32.36 kHz ultrasound is better than that of using 2151 kHz under the same irradiation time and sound density.The effect was significantly enhanced with a small amount of aeration.With a 10 s ultrasonic irradiation pretreatment followed by 20 s UV disinfection ,the inactivation of the total coliforms can reach 4.5 log units, which is superior to the effect of 1 minute UV disinfection which can only get 3.7 log units.Furthermore,the energy consumption of the US coupled with the UV process is lower.